Acceptable aerosol dispensed paint compositions must have sufficient mechanical stability to withstand the mechanical shearing forces which aerosol water based paint compositions normally experience as they are dispensed from conventional aerosol containers. Insufficient stability results in mechanical shearing of polymeric components of the composition. Agglomerated bits of the composition can clog the narrow orifices of the aerosol valve outlet and interfere with the even dispersement of paint. Agglomerated bits can also break away from the orifice and be delivered onto the surface of the substrate being painted, thereby marring the paint film thereon.
Mechanical stability of paint formulations has depended in large measure upon maintaining a solution of the polymer in the aerosolized formulation. Proper mechanical stability and low viscosity have been achieved in solvent based systems employing hydrocarbons, alcohols and other solvents. The volatility of the solvent causes rapid thickening of the paint as the aerosolized composition is dispensed and applied to a substrate. The rapid thickening of the aerosol paint during and after it is dispensed is essential to commercial solvent based paint formulations which must be capable of adhering to vertical surfaces without running. That property of a paint composition is referred to herein as vertical cling.
Although organic solvent based systems have been developed which have good mechanical stability and vertical cling properties, the solvents employed in such systems (e.g., hydrocarbons or alcohols) are flammable, toxic and environmentally undesirable. Thus, it was deemed desirable to develop a water based paint composition which would possess the degree of mechanical stability necessary for it to be dispensed with a minimum of breakup from a conventional aerosol valve, while at the same time possessing a high degree of vertical cling when the composition is sprayed onto a vertical substrate.
In light of the environmental hazards associated with aerosol propellants such as the fluorocarbon propellants, it is also important to employ a propellant which is environmentally safe, and possesses a low degree of flammability when used as a propellant for a water based paint concentrate. The propellant dimethyl ether is environmentally safe and also possesses very low flammability in aqueous systems.
It is an object of this invention to provide an aerosol water based paint composition which employs the environmentally safe and acceptable propellant dimethyl ether, while at the same time possessing the key attributes desired in an aerosol dispensed, water based paint, i.e., mechanical stability, the ability to provide a foam-free durable coherent film on the substrate to which the paint is applied, the ability of the composition to cling to vertical surfaces without running, as well as the ability to provide finished paint films having high gloss.
High gloss aerosol paints have been associated with paints having a low pigment solids content requiring the application of relatively thick films in order to completely cover the substrate with the paint film. The application of thick films, however, raises the problem of running when the paint is applied to vertical substrates. Although as discussed below, the aerosol dispenable water based paints of this invention may be formulated to provide a low gloss (or flat) finish, it was a particular objective of this invention to provide an aerosol dispensable paint formulation exhibiting vertical cling thereby permitting the application of thick films, while at the same time imparting a high gloss finish to the substrate
Aerosol water based paints are disclosed by the patent literature. See, e.g., Page et al. U.S. Pat. No. 4,384,661, U.S. Pat. No. 4,265,797 and U.S. Pat. No. 4,250,253. However, unlike the dimethyl ether propelled compositions of the prior art, the water based paints of this invention employ a thickening agent as a component of the paint concentrate which loses its ability to thicken in the presence of dimethyl ether, but which rapidly regains its ability to thicken upon volatilization and loss of the propellant from the composition during and after the composition is dispensed. Thus, the aerosol water based paint compositions of this invention advantageously possess a relatively low viscosity prior to being dispensed, while thickening rapidly during and after dispensing. The low viscosity prior to dispensing aids in imparting mechanical stability and valve dispensability to the composition, while the thickening of the concentrate upon loss of dimethyl ether aids in imparting vertical cling to the compositions of this invention.